This paper describes the work carried out to extend the NOEL-V platform to include data-level parallelism (DLP) by implementing an integer subset of the RISC-V Vector Extension. The performance and resource utilization efficiency of the resulting vector processor for different levels of DLP (i.e., number of lanes) have been compared to the baseline scalar processor on a Xilinx Kintex Ultrascale field-programmable gate array, employing typical kernels for compute-intensive applications. The role of the memory subsystem has also been investigated, comparing the results obtained with a low-latency and a high-latency main memory. The results show that the speed-up due to the use of the vector pipeline increases with the number of lanes in the vector processor, achieving up to 23.0× the performance of the scalar processor with only 4.3× the resources of the baseline scalar processor. Using an implementation with 32 lanes increases performance even for problem sizes larger than the number of lanes, achieving up to more than 11.7× the performance of the scalar processor with just 1.9× its resource utilization for 128 × 128 matrix multiplications. This work proves that implementations of the selected subset are easily scalable and fit for small-processor implementations in highly constrained space embedded systems.

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This chapter provides an overview of the command and data handling system (CDHS) in small satellites and CubeSats. The chapter presents first analysis of radiation effects, specifically targeted at this subsystem, to justify components and architecture choices. Improvements in radiation testing strategies are also presented, specifically for small satellites. State-of-the-art components are then presented, providing an overview of the current market and the most common architectures. An overview of past and current missions is also presented, providing a clear mapping of the presented state-of-the-art components and architectures to guide future designs. High-level design considerations are also presented to help the reader follow some of the current trends in the sector. This chapter, overall, aims at presenting the most common approaches for the CDHS system and comparing this with traditional satellites, showing where the main differences lay with component selection and testing strategies being the fundamental points driving the architecture choices.

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The usage of terrestrial processors in space applications is not straightforward, as processors in space face unique challenges due to the effects of the space environment, like ionizing radiation causing Single Event Effects (SEEs). In the nineties, the European Space Agency chose the Scalable Processor ARChitecture (SPARC) Instruction Set Architectures (ISA) for its processors, as it was the only solution available at that time providing both openness and available software support in terrestrial applications. Currently, a large part of the worldwide space community is using SPARC-based radiation-hardened (rad-hard) or radiation-tolerant (rad-tol) LEON processors in ongoing and planned missions, although SPARC processors virtually disappeared from terrestrial applications. Rad-hard and rad-tol processors for space applications typically lag more than a decade behind their commercial counterparts in terms of performance and the gap is widening every year. This is mainly due to the use of Rad-Hard-By-Design (RHBD) cells and older technology nodes. The larger vulnerability to SEEs of complex microarchitectures is not the only reason why simple microarchitectures with low parallelism are still the vast majority of processors employed in space. As a matter of fact, most of the tasks executed by processors in space data systems are non-compute-intensive workloads. The reason is that they are mainly employed for non-demanding control and housekeeping operations. Therefore, enabling demanding tasks, such as the execution of Artificial Intelligence (AI) algorithms in space embedded systems, requires a large leap in spacegrade processors, especially because space data systems in satellites are typically powerconstrained. Recently, RISC-V, a novel free and open ISA, has risen in popularity in terrestrial applications, drawing the attention of several universities and companies. Given the similarity between SPARC and RISC-V, this dissertation starts by analyzing the advantages of using RISC-V in space applications. The openness of RISC-V already enabled a vast field of research activities for terrestrial applications, with many tools and models at different level of abstraction already available. Therefore, the space industry can spin-in developments from academia and industry, focusing efforts mainly on improvements concerning specific needs in space applications and without wasting efforts on other activities. In order to fully exploit modularity, the need of defining the types of processors required in space application was identified in this dissertation. The modularity of RISC-V was employed to identify several applications in space data systems and RISC-V processor profiles to address them. They were defined in this work by the ISA subset, Instruction-Level Parallelism (ILP), Data-Level Parallelism (DLP), Processor- Level Parallelism (PLP), reference implementation and expected performance. The processors profiles defined range from microcontrollers to general-purpose implementations to high-performance processors for AI. Finally, a roadmap to bring RISC-V IP cores for terrestrial applications to space level was defined, identifying the steps and models required. After the thorough analysis of the state-of-the-art of RISC-V processors was completed, two different sets of activities were identified…@en

Integrated circuits employed in space applications generally have very low-volume production and high performance requirements. Therefore, the adoption of Commercial-Off-The-Shelf (COTS) components and Third Party Intellectual Property cores (3PIPs) is of extreme interest to make system design, implementation and deployment cost-effective and viable w.r.t. performance. On the other hand, this design paradigm exposes the system to a number of security threats both at design-time and at runtime. In this paper, we discuss the security issues related to space applications mainly focusing on threats that come from the adoption of the well-known RISCV microprocessor. We highlight how Hardware Trojan horses (HTHs) and Microarchitectural Side-Channel Attacks (MSCAs) may compromise the overall system operation by either altering its nominal behavior or by stealing secret information. We discuss the security extensions provided by the RISC-V architecture as well as their limitations. The paper is concluded by an overview of the issues that are still open regarding the security of such microprocessor in the space domain.

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Soft errors in embedded systems' memories like single-event upsets and multiple-bit upsets lead to data and instruction corruption. Therefore, devices deployed in harsh environments, such as space, use fault-tolerant processors or redundancy methods to ensure critical application dependability. Another rising concern in secure, critical space applications is the possible introduction of hardware Trojans in an untrusted phase of the manufacturing process. Besides environmental side-effects, an adversary that has injected a malicious mechanism e.g., in the processor or memory can trigger unwanted behavior or leak sensitive information. Techniques to prevent or mitigate hardware Trojans are important to ensure hardware security. Leveraging the openness of the RISC-V ISA, this paper introduces a novel solution to improve the security and dependability of softcores with a low area and latency overhead. The instruction validator which is the first part of this solution can effectively detect hardware Trojans and multiple-bit upsets in the instruction memory by checking instruction/address pairs using a Bloom filter probabilistic data structure. The second part of the solution is the proposal of an error correction code instruction memory using Hamming single-error correction to detect and correct single-event upsets. It has also been proven that the Hamming decoder improves the detection performance of the instruction validator.

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RISC-V is an open and modular Instruction Set Architecture(ISA) which is rapidly growing in popularity in terrestrial applications. This paper presents the place in future space embedded systems ESA's roadmap for RISC-V based processors. In order to satisfy different applications with contrasting requirements in satellite data systems, four different types of processors are identified: 1) General-Purpose (GP) processors for payloads 2) main platform On-Board Computers (OBCs) controllers 3) low-area/low-power microcontrollers (uCs), 4) enhanced payload processors with support for Artificial Intelligence (AI). We also describe the state of the art of the RISC-V software ecosystem, including the currently available hardware platforms, with a focus on developments for space applications and what has already been done in the European Space Industry. Finally, planned activities are presented, with a focus on the role of the European ecosystem.@en

This paper discusses principles and techniques to evaluate processors for dependable computing in space applications. The focus is on soft errors, which dominate the failure rate of processors in space. Error, failure and propagation models from literature are selected and employed to estimate the failure rate due to soft errors in typical processor designs. A similar approach can be followed for applications with different radiation environments (e.g. automotive, servers, experimental instrumentation exposed to radiation on ground), by adapting the error models. This detailed white-box analysis is possible only for open-source Intellectual Property (IP) cores and in this work it will be applied to several open-source IP cores based on the RISC-V Instruction Set Architecture (ISA). For these case studies, several types of redundancy described in literature for space processors will be evaluated in terms of their cost-effectiveness and expected final in-orbit behavior. This work provides a comprehensive framework to assess efficacy and cost-effectiveness of redundancy, instead of listing and categorizing the techniques described in literature without assessing their relevance to state-of-the-art designs in space applications.

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The use of deep neural networks (DNNs) in terrestrial applications went from niche to widespread in a few years, thanks to relatively inexpensive hardware for both training and inference, and large datasets available. The applicability of this paradigm to space systems, where both large datasets and inexpensive hardware are not readily available, is more difficult and thus still rare. This paper analyzes the impact of DNNs on the system-level capabilities of space systems in terms of on-board decision making (OBDM) and identifies the specific criticalities of deploying DNNs on satellites. The workload of DNNs for on-board image and telemetry analysis is analyzed, and the results are used to drive the preliminary design of a RISC-V vector processor to be employed as a generic platform to enable energy-efficient OBDM for both payload and platform applications. The design of the memory subsystem is carried out in detail to allow full exploitation of the computational resources in typically resource-constrained space systems.

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The aim of this paper is to assess the feasibility and on-board hardware performance requirements for on-board telemetry forecasting by implementing a Recurrent Neural Network (RNN) on low-cost multicore RISC-V microprocessor. Gravity field and steady-state Ocean Circulation Explorer (GOCE) public telemetry data was used for training RNNs with different hyperparameters and architectures. The prediction accuracy of these models was evaluated using mean error and R-squared score on the same test dataset. The implementation of the RNN on a RISC-V embedded device, representative of future space-grade hardware, required some adaptations and modifications due to the computational requirements and the large memory footprint. The algorithm was implemented to run in parallel on the 8 cores of the microprocessor and tiling was employed for the weight matrices. Further considerations have also been made for the approximation of sigmoid and hyperbolic tangent as activation functions.@en

A new methodology for Total Ionizing Dose (TID) tests is proposed. It is based on the employment of an on-chip ⁹⁰ Sr/ ⁹⁰ Y beta source as alternative to standard methods such as ⁶⁰ Co gamma rays and electrons from LINAC. The use of a compact beta source for TID tests has several advantages. In particular, the irradiation of devices with more than one radiation source results in a better representation of the complex space radiation environment composed of several types, energies and dose-rates. In addition, the use of an easy handling beta source allows the irradiation of electronic devices without any damage to other auxiliary circuit. In this work, ⁹⁰ Sr/ ⁹⁰ Y beta source dosimetry and related radiation field characteristics are discussed in depth. In order to validate the proposed source for TID tests, a rather complex device such as the “SPC56EL70L5” microcontroller from ST-Microelectronics was exposed to ⁹⁰ Sr/ ⁹⁰ Y beta rays. The results of this test were compared to that of a previous test of another sample from the same lot with a standard gamma ⁶⁰ Co source. The electronic performances following the two irradiations have been found to be in excellent agreement, by demonstrating therefore the validity of the proposed beta source for TID tests.

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This paper proposes a roadmap to address present and future needs in space systemswithRISC-Vprocessors. RISCVis an open and modular instruction set architecture, which is rapidly growing in popularity in terrestrial applications. To satisfy different applications with contrasting requirements in satellite data systems, four different types of processors are identified: 1) low-area/low-power microcontrollers, 2) on-board computers, 3) general-purpose processors for payloads, and 4) enhanced payload processors for artificial intelligence. Several solutions based onRISCVare proposed for eachof these types of processors and comparedwith proprietary commercial-off-the-shelf andspacegrade solutions. An extensive analysis of the results available fromliterature is conducted to show that RISC-V has the potential to solve such a wide range of needs. This paper will also show the unprecedented number of open-source implementations and models that were developed in a relative short time on a single instruction set architecture. Future space systemscouldbenefit frommanyof those developments, andthisworkidentifies andhighlightswhat is stillmissing to satisfy the specific needs of processors for space, especially in terms of fault tolerance and technology readiness level. @en

This paper analyzes the contribution of caches to failures at processor level due to soft errors. In order to do this, approximated methodologies to estimate the percentage of the total Sensitive Area (SA) of a processor for each unit during early design exploration are proposed. Then, to identify the most vulnerable units, a metric called Relative Soft Error Vulnerability (RSEV) is defined. The analysis shows that caches are the most vulnerable units of state-of-the-art processors and that, even when considering higher-frequency and more complex pipelines representative of next-generation processors for space applications, the final in-orbit failure rate is dominated by failures caused by upsets in cache arrays. Even when protecting memory arrays with information redundancy, the large fraction of upsets occurring in caches is potentially the biggest threat to processor availability and reliability, especially if errors are modelled with invalid assumptions and are not properly handled when detected.

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This paper presents preliminary position on the use of the novel, free and open RISC-V Instruction Set Architecture (ISA) for on-board electronics in space. The modular nature of this ISA, the availability of a rich software ecosystem, a rapidly growing community and a pool of open-source IP cores will allow Space Industry to spin-in developments from terrestrial fields (in terms of security, artificial intelligence, support for operating systems, hardware acceleration etc.) while focusing its efforts mainly on aspects related to the specific needs of on-board electronics for space applications (e.g. fault tolerance, observability, error signaling, etc.). This will improve reuse and avoid the necessity of developments from scratch when not strategically needed, eventually increasing productivity and reducing costs. The use of an open, non proprietary ISA will allow ad-hoc design of microarchitecture-level soft error countermeasures that can greatly increase the robustness of Application Specific Standard Products (ASSP) and FPGA implementations.

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The tolerance to the cumulative effects of ionizing radiation is one of the most important parameters to keep into account when selecting an EEE component for space applications. TID sensitivity is normally investigated measuring changes induced by gamma rays from 60Co sources to nominal parameters of a component or to its expected functional behavior. In this work we propose an on-chip 90Sr/90Y electron source as an alternative methodology for TID tests.60Co and 90Sr/90Y TID test setups for a complex SoC are compared in terms of complexity and of experimental results, investigating the use of a 90Sr/90Y as well as the established 60Co. We show that 90Sr allows a simpler test setup, manages to reproduce specific modes of failure obtained with 60Co and causes failures at comparable total doses. This makes 90Sr an interesting alternative to 60Co qualification and the use of untested components, to be further investigated especially for complex COTS SoCs.@en

The use of System-on-Chip (SoC) solutions in the design of on-board data handling systems is an important step towards further miniaturization in space. However, the Total Ionizing Dose (TID) and Single Event Effects (SEE) characterization of these complex devices present new challenges that are either not fully addressed by current testing guidelines or may result in expensive, cumbersome test configurations. In this paper we report the test setups, procedures and results for TID testing of a SoC microcontroller both using standard C60o and low-energy protons beams. This paper specifically points out the differences in the test methodology and in the challenges between TID testing with proton beam and with the conventional gamma ray irradiation. New test setup and procedures are proposed which are capable of emulating typical mission conditions (clock, bias, software, reprogramming, etc.) while keeping the test setup as simple as possible at the same time.@en